Photoresist dispense method by compensation for substrate reflectivity

ABSTRACT

In the manufacture of a semiconductor device, a method for forming a layer on a semiconductor substrate compensates for variations in wafer substrate reflectivity. The method includes providing substrate illumination and then adjusting the illumination on the substrate. The method also includes controlling the dispensation of material over the substrate as a function of the adjusted illumination. By compensating for variations in wafer substrate reflectivity, manufacturing processes can realize more consistent photoresist coatings on wafer substrates from one wafer lot to another.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor devices andtheir fabrication and more particularly to a method of applyingphotosensitive material to a semiconductor wafer.

BACKGROUND OF THE INVENTION

The electronics industry continues to rely upon advances insemiconductor technology to realize higher-functioning devices in morecompact areas. For many applications, realizing higher-functioningdevices requires integrating a large number of electronic devices into asingle silicon wafer. As the number of electronic devices per given areaof the silicon wafer increases, the manufacturing process becomes moredifficult.

A large variety of semiconductor devices have been manufactured havingvarious applications in numerous disciplines. Such silicon-basedsemiconductor devices include, among others, metal-oxide-semiconductor(MOS) transistors, such as p-channel MOS (PMOS), n-channel MOS (NMOS)and complimentary MOS (CMOS) transistors, bipolar transistors, andBiCMOS transistors. Each of these semiconductor devices generallyincludes a semiconductor substrate on which a number of active devicesare formed. The particular structure of a given active device can varybetween device types. For example, in MOS transistors, an active devicegenerally includes source and drain regions and a gate electrode thatmodulates current between the source and drain regions.

Elements in semiconductor devices are typically formed in the siliconthrough the use of well-known deposition, photolithography and etchingtechniques. The processing of a silicon wafer typically includes acoating step in which a photoresist solution is applied to the wafer.The purpose of the coating step is to apply a uniform polymeric film ofselected thickness onto the wafer. This technique is commonly known asspin coating, which involves dispensing the photoresist solution ontothe wafer and rapidly spinning the wafer. Spinning the wafer serves todry the photoresist into a solid or gel layer having the desired filmthickness.

The dispensing step is performed by distributing photoresist solutionover the entire wafer before the wafer is spun (static dispense) or byapplying a small quantity of solution near the center of the wafer whilespinning the wafer to distribute the solution (dynamic dispense). Duringthe dispensing step, it is desired to distribute the solution uniformlyonto the wafer to allow the formation of a coat of uniform thicknessduring the spin step. The dispensing apparatus should be maintained at apre-defined, relatively close distance from the wafer to preventsplashing of the solution. Advanced photoresist dispensing methods havevaried wafer rotation speed during chemical delivery of the spin coatingcycle in order to achieve uniform photoresist coatings with minimal lossin photoresist material. However, this approach has not always beensufficiently precise in forming the photoresist layer.

In an effort to improve these systems, a light source has been includedin the system that is directed at the substrate so that light isreflected up for detection by a camera. Variations in the wafer surfacelead to variations in the light reflected. When the camera senses thatthe substrate is dark (less light reflected up to the camera), morephotoresist material is dispensed. The opposite is also true; lessphotoresist is dispensed if the light reflected off the substrate is toobright. However, the process for depositing photoresist is problematicwhen the light reflected from the substrate is too dim or the lightappears washed out. Variations in wafer surface reflectivity have madeit difficult to reproduce from one wafer lot to another, a photoresistlayer on a wafer substrate that has a uniform thickness across the wafersurface while at the same time minimizing the required amount ofphotoresist being dispensed.

Accordingly, there has been a long-standing need for semiconductormanufacturing processes that can overcome the aforementioneddisadvantages of the prior art.

SUMMARY OF THE INVENTION

In connection with the present invention, it has been discovered thatsignificant advantages can be gained by precisely detecting when thephotoresist material comes into contact with the wafer and using thisdetection to compensate for variations in substrate reflectivity.Variations in substrate reflectivity cause variations in the detectionof the moment of initial photoresist deposition, leading to variationsin photoresist layer thickness and uniformity across the wafer surface.The present invention will help to compensate for variations in wafersubstrate reflectivity that will lead to photoresist coating on wafersubstrates that is consistent from one wafer lot to another.

The present invention is exemplified in a number of implementations andapplications, some of which are summarized below. According to anexample embodiment, in the manufacture of a semiconductor device amethod is provided for forming a layer over a semiconductor substratethat includes providing substrate illumination and then adjusting theillumination on the substrate. The method also includes controlling thedispensation of material over the substrate as a function of theadjusted illumination.

In another example embodiment, an apparatus for forming a layer on asemiconductor substrate is disclosed. The apparatus includes a device,such as a light, for illuminating a substrate and a mechanism foradjusting the illumination on the substrate, wherein the adjustmentmechanism is coupled to the substrate illumination device. The apparatusalso includes a controller for dispensation of a material over thesubstrate as a function of the adjusted illumination, wherein thecontroller is coupled to the adjustment mechanism.

The above summary of the present invention is not intended to describeeach illustrated embodiment or every implementation of the presentinvention. The figures and detailed description that follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 illustrates an example embodiment of a material deposition systemfor semiconductor wafer substrates that is arranged to measure lightreflected from a substrate, made in accordance with the teachings of thepresent invention;

FIG. 2 illustrates the system of FIG. 1 that is arranged to adjust thereflectivity of light from the substrate to a predetermined level, madein accordance with the teachings of the present invention;

FIG. 3 illustrates the system of FIG. 2 that is arranged to dispense thephotosensitive material after the substrate reflectivity has beenadjusted, made in accordance with the teachings of the presentinvention; and

FIG. 4 illustrates an example embodiment of a material deposition systemfor semiconductor wafer substrates located within an enclosed area, madein accordance with the teachings of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is believed to be applicable to a variety ofdifferent types of semiconductor devices and the manufacturing processesrelated thereto. The present invention has been found to be particularlysuited for forming photoresist layers on substrates that have consistentthickness and uniformity across the wafer surface from lot to lot. Whilethe present invention is not necessarily limited to such devices andprocesses, various aspects of the invention may be appreciated through adiscussion of various examples using this context.

In connection with an example embodiment of the present invention, amethod is provided for forming a layer over a semiconductor substrate.The method includes providing substrate illumination and then adjustingthe illumination on the substrate. The method also includes controllingthe dispensation of material over the substrate as a function of theadjusted illumination.

In another example embodiment, an apparatus for forming a layer over asemiconductor substrate is disclosed. The apparatus includes a devicefor illuminating a substrate and a mechanism for adjusting theillumination on the substrate, wherein illumination adjustment mechanismis coupled to substrate illumination device. The apparatus also includesa controller for dispensation of a material over the substrate as afunction of the adjusted illumination, wherein the controller is coupledto illumination adjustment mechanism.

Referring now to the drawings, FIG. 1 illustrates one embodiment of thepresent invention that addresses the issue of layer formationuniformity. Material deposition system 30 includes a wafer substrate 32,disposed on a spinning mechanism 33, a nozzle 34 for dispensing of amaterial (such as a photoresist), a light source 36 and a camera 38 (orany other photographic device or imaging mechanism). In this example,camera 38 is a digital camera. System 30 further includes a lightdetecting device 40, such a photodiode detector shown in this exampleembodiment, that is coupled to a light source controller 42. Lightsource controller 42 is also coupled to light source 36 and controls theintensity of light 44 in response to the reflected light received atphotodiode 40.

Referring to FIG. 2, light 44 is adjusted to a predetermined leveldepending on the amount of light reflected from substrate 32 that isdetected by photodiode detector 40. Photodiode detector 40 is in thesystem to check the substrate reflectivity of each substrate prior tophotoresist material dispensing. The amount of light reflected dependson the wafer surface topography. Upon receiving a signal from photodiode40, light source controller 42 then signals a change to light source 36.This results in a new light intensity 44A to be directed at thesubstrate, set to a predetermined level, which optimizes the light beingreflected from the substrate.

Referring to FIG. 3, after the light intensity has been optimized thenext step in the process is to dispense photoresist material 48 fromnozzle 34 onto substrate 32. The photoresist can be deposited whilesubstrate 32 is stationary, for a static dispense, or while thesubstrate is being spun by spinning mechanism 33, for a dynamicdispense, depending on what the specifications require for photoresistlayer thickness. When photoresist material 48 makes contact withsubstrate 32, camera 38 will detect this event. The timely detection ofmaterial 48 making contact with substrate 32 will ensure that the properamount of photoresist is deposited.

In order to prevent contamination of the photoresist layer or preventoutside spraying of photoresist material during the spinning cycle, thematerial deposition system may be located in an enclosed area. Theenclosed area is usually comprised of walls that are a series of windowsthat are either reflective and/or transparent. This type of arrangementallows stray light from internal and external sources to be reflectedback to the substrate surface, thereby distorting the reflectivitymeasurements that are being taken by the detection system at the startof the photoresist deposition process. External light usually penetratesone or more of the enclosed area glass walls and reflects off of thesubstrate. The camera then detects additional light coming from thesubstrate and proceeds to signal a change to the deposition nozzle thatwill lead to less photoresist material being dispensed on the substrate.

Referring to FIG. 4, a second example embodiment is illustrated forcontrolling the illumination level of the light that is being reflectedfrom the substrate in order to promote consistent substrate reflectivitymeasurements by the detection system. Photoresist material depositionsystem 30 can be located within an enclosure 60 that is comprised ofwalls that have surfaces that have been coated with non-reflectivematerial. External source of light 52 has light waves 54 reflected offone of the walls to prevent it from passing through and being reflectedoff substrate 12, thereby distorting the amount of light being detectedby camera 18. Further, the internal light source 16 has light waves 20either illuminating substrate 12 or having stray waves absorbed by oneof the walls of enclosure 60 to prevent light from coming back to thesubstrate and distorting the amount of light being detected by camera18. One of the walls can include a reduced transparent window area 62,which can be in the form of a slit, for viewing the photoresistdeposition process. In various embodiments, camera 18 is a digitalcamera and can also be a conventional non-digital camera.

In yet another embodiment, enclosure 60 provides the capability ofcontrolling 8 the light that is being reflected off the substrate toimprove the overall material deposition system. Such control isadvantageous to enhance the uniformity of the resulting photoresistlayer without the costs of retrofitting the system with a controller anda photodiode. In this embodiment, enclosure 60 could easily be used in acurrent photoresist deposition system that uses a light detection systemto determine when the photoresist material makes contact with thesubstrate. Where more precision is required in forming the photoresistlayer, system 30 is located within enclosed area 60 to further controlthe light that is being reflected from the substrate. In yet anotherembodiment, system 30 and enclosure 60 could also be used in othercoating processes, either together or separately, where light reflectedfrom a substrate is used to detect a particular processing event.

The present invention is not limited to photoresist materials and can beused when a substrate is to be coated with a particular material.

While the present invention has been described with reference to severalparticular example embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention, which is set forth in the followingclaims.

What is claimed is:
 1. In the manufacture of a semiconductor device, amethod for forming a layer over a semiconductor substrate, comprising:providing illumination on the substrate; adjusting the illumination; andcontrolling the dispensation of a material over the substrate as afunction of the adjusted illumination.
 2. The method according to claim1, wherein adjusting the illumination includes detecting theillumination, and measuring light that is reflected from the substrate.3. The method according to claim 1, further including adjusting theillumination of the substrate to an optimum level of substratereflectivity.
 4. The method according to claim 3, wherein controllingdispensation of material includes: dispensing the material after thesubstrate reflectivity has been optimized; and detecting when thedispensed material contacts the substrate.
 5. The method according toclaim 1 wherein adjusting the illumination includes: detecting a levelof substrate reflectivity; and optimizing the level of substratereflectivity by adjusting the intensity of substrate illumination. 6.The method according to claim 2, wherein detecting the illuminationincludes using a photodiode detector.
 7. The method according to claim6, wherein controlling the dispensation includes coupling a light sourceto the photodiode detector.
 8. The method according to claim 2, whereincontrolling the dispensation includes defining a light-controlledenvironment and optimizing the illumination on the substrate to a givenlevel of substrate reflectivity.
 9. The method according to claim 8,wherein the light-controlled environment includes providing an enclosurefor forming therein the layer over the substrate, the enclosureincluding walls having a non-reflective material coating thereon. 10.The method according to claim 1, further including adjusting theillumination after forming a first layer on the substrate prior toforming a second layer over the semiconductor substrate.
 11. A methodfor forming a layer over a semiconductor substrate, comprising:providing illumination on the substrate; detecting a level of substratereflectivity; optimizing the level of substrate reflectivity byadjusting the intensity of substrate illumination; dispensing a materialover the substrate after the substrate reflectivity has been optimized;and detecting when the dispensed material makes contact with thesubstrate.
 12. The method according to claim 11, wherein detecting thesubstrate reflectivity includes using a photodiode detector.
 13. Themethod according to claim 11, further including providing an enclosurefor forming therein the photoresist layer on the substrate, theenclosure including walls having a non-reflective material coatingthereon, whereby signal noise is reduced and substrate reflectivitymeasurement is improved.
 14. The method according to claim 13, whereinone of the walls has a reduced transparent window area for viewing thephotoresist layer deposition.
 15. The method according to claim 1,wherein the step of controlling the dispensation of a material includescontrolling the dispensation of a photoresist material.
 16. The methodaccording to claim 1, wherein the step of adjusting the illuminationincludes providing a light source controller coupled to a lightdetector.
 17. The method according to claim 4, further including thestep of providing an imaging device for detecting when the dispensedmaterial contacts the substrate.